A Nonfused Ring Electron Acceptor with Aggregation-Induced Emission Assistance Achieving Over 20% Efficiency in Organic Solar Cells

The development of nonfused ring electron acceptors (NFREAs) with high electroluminescence quantum efficiency (EQE_EL) is essential for advancing the commercialization of organic solar cells (OSCs), due to their low-cost and minimal energy losses (E_loss). However, designing such NFREAs remains a significant challenge. Herein, we present a medium-bandgap NFREA, TT-TCBr, which exhibits a high EQE_EL of 1.0 × 10⁻³ and an excellent electron mobility of 1.5 × 10⁻⁴ cm² V⁻¹ s⁻¹. Interestingly, TT-TCBr shows enhanced photoluminescence quantum yield from solution (9.24%) to film (20.7%). In OSCs, the D18:TT-TCBr-based OSC achieves a good power conversion efficiency (PCE) of 13.20% with a high open-circuit voltage of 1.09 V and a low nonradiative energy loss of 0.177 eV. Importantly, TT-TCBr shows good miscibility with L8-BO, leading to an increased exciton diffusion length and EQE_EL in the L8-BO: TT-TCBr blend. When TT-TCBr is introduced as a guest molecule into the D18:L8-BO-based OSC, E_loss is reduced from 0.543 to 0.530 eV, resulting in a significantly increased PCE from 19.16% to 20.10%, which represents one of the highest PCEs reported for OSCs. This research will significantly contribute to the advancement of high-performance guest materials for the rapid development of single-junction OSCs.